1. Field of the Invention
The present invention relates to an electroluminescent (EL) lamp having indexation indicium thereon, and to an appertaining method of manufacture of an electroluminescent lamp wherein the registration of component layers and elements of the lamp is readily effected via utilization of such indexation indicia.
2. Description of the Related Art
Electroluminescent lamps are extensively used as illumination sources in a wide variety of applications and products, including primary, emergency and auxilliary lighting systems in land-based vehicles, building structures, aircraft, marine craft, and outdoor locations.
Structurally, electroluminescent lamps typically comprise a layer of electroluminescent phosphor material, such as a metal activated zinc sulfide, which is fixed by a polymer binder between two conductive layers, one of which is transparent. When an alternating electric field is applied across the conductors, the electroluminescent phosphors are excited and emit photons, with almost all of the radiated energy lying within the visible light spectrum. The emission spectrum and wavelength generated by the electroluminescent phosphors are controlled by an activator, such as copper or manganese.
Electroluminescent phosphors are inherently hygroscopic in character. Exposure to excess heat and moisture will damage the electroluminescent phosphor particles. This sensitivity to heat and moisture is so strong that exposure to even low humidity conditions will adversely affect the illumination efficiency and decrease the light output capacity of a lamp in which such exposed electroluminescent phosphors are incorporated.
A number of different methods have been used in order to reduce the exposure of the electroluminescent phosphor particles to these detrimental effects. One such method attempts to encapsulate each individual electroluminescent phosphor particle. Although this approach has had limited success, the EL industry has been slow to adopt same.
The most common method of moisture protection of electroluminescent phosphor particles is packaging the lamp structure that contains the electroluminescent phosphors, in a transparent, moisture impenetrable polymer material. Polychlorotrifluoroethylene (PCTFE) copolymers are the most moisture-impenetrable, transparent polymers known. They have moisture vapor transmission rates that are an order of magnitude below all other transparent polymers. While the use of a PCTFE film provides the best moisture protection and subsequently the longest life electroluminescent lamps, it also significantly complicates the lamp manufacturing process.
In the manufacture of electroluminescent lamps, the typical lamp has an aluminum foil substrate which is coated with an insulating layer of high dielectric constant material, such as a high dielectric resin loaded with barium titanate, and is subsequently coated with a high dielectric resin loaded with electroluminescent phosphor.
The resulting electroluminescent phosphor coated foil is screen printed with a transparent electrode layer, using a transparent conductive coating. Next, a narrow conductive busbar is formed using a silver-loaded ink that is screen printed onto the transparent electrode, so that the busbar subsequently may be used to efficiently transfer current to all points of the transparent electrode layer.
A desiccant layer then is applied over the electrode and busbar. The desiccant can either be pattern printed as described in U.S. Pat. No. 5,051,654, the disclosure of which is hereby incorporated herein by reference in its entirety, or else the desiccant can be laminated to the electrode layer. This coated foil assembly is next cut to a prescribed shape using appropriate cutting/shaping tools, such as a shear cutter, a die cutter, or a router.
The resulting cut assembly must have electrical leads placed onto it to transfer current from outside the final package to the electrodes of the lamp assembly. The leads are hand placed into position. To manually place leads when the desiccant is laminated to the transparent electrode, the edge of the desiccant must be pulled back, an insulating tape must be put over the edge of the foil where the front lead will be placed, the front lead must be positioned onto the busbar, and the desiccant must be resealed in place. These fabrication steps are all done by hand.
If the desiccant is screen printed, an edge tape must be placed over the edge of the lamp and the lead must be hand- or machine-positioned on the busbar. After lead placement is complete, the lamp must be packaged and dried.
Regardless of whether the desiccant is screen printed or laminated, the fabrication steps are extremely labor intensive and time consuming. An efficient automated process therefore would significantly reduce labor costs for the lamp manufacturing process, permitting a much more economic electroluminescent lamp product to be produced, as well as achieving a vast increase in the production rate of the electroluminescent lamps, since the manual process steps involved in current fabrication methods greatly restrict the product output of the lamp manufacturing facility.
To subsequently package an electroluminescent lamp in PCTFE, small pieces of pressure-sensitive two-sided tape are placed on the back of the lamp, then the lamp is stuck to the back package material, a PCTFE film. The front package material is positioned over the front of the lamp and then heat tacked to the back package material, thereby sandwiching the lamp assembly between the front and back package layers.
When the lamp is finally "laid up," in the above-described manner, it is allowed to dry in a low humidity room. Once dry, the lamp is heat- and pressure-sealed in the final sealed assembly which has been cut to create the finished lamp. The final cutting operation requires hand alignment or extensive programming on a CNC router. This final cutting step also is very labor- and time-intensive.
Thus, the conventional prior art method of manufacturing electroluminescent lamps is labor intensive and time-consuming, requiring much inherently slow hand manipulation of the parts that comprise the final product. The hand processing steps involved in electroluminescent lamp manufacture, which result in low manufacturing efficiency, are not amenable to automated production due to the lack of suitable guide means for the processing of electroluminescent lamp assembly during its fabrication.
As a result, a great deal of time, effort, and resources have been expended in efforts to improve the electroluminescent lamp manufacturing process. For nearly thirty years, there have been repeated efforts to efficiently automate and improve the manufacture of electroluminescent lamps. During this period of time, some manufacturing solutions have been found which improve the processing per se of electroluminescent lamps, but always at the expense of lamp quality.
In one approach proposed by the prior art, the electroluminescent lamp is completely printed, i.e., all the layers of the lamp are printed onto a stable polymeric substrate which functions as the back package of the lamp. The resulting printed structure then is laminated to the front package and cut in reference to visible registration marks that are located on the surface of the laminated structure, but outside the dimensions of the final cut of the lamp.
The resulting electroluminescent lamp is characterized by extremely poor service life, because the package materials do not have effective water vapor impermeability properties. As mentioned earlier herein, PCTFE copolymers are the most moisture-impenetrable, transparent polymers known, with very low moisture vapor transmission rates. However, PCTFE film cannot be used in an "all-printed" lamp process, because the surface energy of the PCTFE film is too low to print on and because the PCTFE material is unstable and shrinks at the elevated temperature levels used to dry the various inks used in the all-printed electroluminescent lamp.
For these reasons, the all-printed electroluminescent lamp typically uses polyethylene terephthalate (PET) film as its substrate. While PET film is stable and can be made printable in character, such film nonetheless has water vapor transmission properties orders of magnitude worse than PCTFE film. A direct correlation exists between lamp life and the amount of water vapor and atmospheric gases that reach the phosphor layer while the lamp is charged. The more atmospheric moisture permeates into the interior portions of the electroluminescent lamp, the lower is the service life of the electroluminescent lamp. Thus, conventional all-printed electroluminescent lamps using PET film as its packaging material, is characterized by extremely short lamp life and poor quality.
In efforts to improve on the all-printed electroluminescent lamp manufacturing process, attempts have been made to encapsulate the individual phosphor particles, to provide improved moisture and gas protection of the active illuminating material. These attempts, however, have been relatively unsuccessful.
Although the use of encapsulated phosphors does improve electroluminescent lamp life in comparison to corresponding electroluminescent lamps fabricated with nonencapsulated phosphors, an electroluminescent lamp containing encapsulated phosphors and sealed in PET film generally has a shorter service life than a corresponding electroluminescent lamp containing nonencapsulated phosphors and sealed in a PCTFE film.
Thus, while some measurable improvement is afforded by an encapsulated phosphor particle construction in enhancing the moisture-resistance of the phosphors, such enhancement of moisture-resistance is not enough to improve the service life of the all-printed electroluminescent lamp when compared with the service life of a typical electroluminescent lamp sealed in a PCTFE film. Further, the encapsulation of the phosphor particles increases the complexity and cost of the resulting electroluminescent lamp product.
Each of the foil, electrode, dielectric, phosphor, busbar, desiccant, etc. layers in the electroluminescent lamp construction may constitute a lamina for a single lamp article, so that one product lamp article is formed from a single laminate assembly of multiple laminae.
Alternatively, each of such constituent layers may be of an extended sheet conformation, and have a multiplicity or array of appertaining lamp-forming regions thereon of the desired character, so that a number of discrete lamp articles may be formed from the stacked laminate comprising the respective sheets. Such methodology may be particularly advantageous in an all-printed lamp manufacture, since the individual sheets can be each printed across the full surface of the sheet, so that the final assembled laminate has discrete surface areas constituting individual lamp articles, which then can be cut from the assembled laminate, to yield the lamp articles for further processing and packaging.
Regardless of the specific method of manufacture described above, a lamp article, comprising the electroluminescent phosphor coated foil, transparent electrode layer, transparent conductive coating, conductive busbar, and desiccant layer, must subsequently be cut to a prescribed shape using cutting/shaping tools. In such cutting/shaping operation, the registration of the cutting means is critical, since any misalignment of the cutter, in relation to the sucessively layered elements in the laminated lamp assembly, can lead to the cutter severing the individual lamp article inside its intended marginal edges, thereby rendering the lamp article useless for its intended purpose and necessitating its rejection in the manufacturing process.
The registration problems discussed above have proven especially intractable. Although the prior art has provided registration marks at the margins of the film stock or layers from which the laminated lamp article is cut, such marks reside outside of the lit area of the lamp. Accordingly, once the lamp is cut and separated from the scrap containing the registration mark-containing margin, the lamp thereafter lacks any associated registration indicia which would serve as an alignment guide in the further processing of the lamp. The further processing steps, involving heat and pressure sealing and packaging of the lamp, followed by the final (finishing) cutting of the lamp product article, require close alignment of the lamp with the processing equipment, and any mis-registration may impair or even fully ruin the product article, as noted hereinabove.
These registration problems have not been satisfactorily resolved by the art, and in practice the rate of rejection of mis-registered product articles is unacceptably high.
Thus, the fact is that the lack of any reliable means or method of aligning the electroluminescent lamp assembly in its final packaging and cutting steps, so that the illuminated or lit area of the lamp (such "illuminated or lit area" being the phosphorluminescent region of the laminated assembly, i.e., the light-producing portion containing the phosphor material)is appropriately positioned inside the intended margins of the lamp article, has posed a continuing impediment to the efficient high volume commercial manufacture of electroluminescent lamp articles.
It would therefore be a significant advance in the art, and is accordingly an object of the present invention, to provide an electroluminescent lamp construction and method of manufacture which overcomes the aforementioned deficiencies of the prior art.
Other objects and advantages of the present invention will more fully apparent from the ensuing disclosure and appended claims.